The present invention relates generally to household refrigerators and, more particularly, to a refrigerator operating mode appropriate for an extended period of zero usage such as would occur when a user is on vacation.
Modern automatically-defrosting refrigerators are designed to provide proper and efficient operation during normal usage conditions. During normal usage conditions, temperatures within the refrigerated compartments are maintained at levels appropriate for safe storage of food. The frequency of or, expressed alternatively, the interval between successive automatic defrosting operations is selected to avoid unnecessary defrosting operations and to prevent excessive accumulation of frost on the evaporator under reasonably expected humidity loading conditions. Further, many modern refrigerators include automatic icemakers connected to household water supply lines to conveniently provide a ready supply of ice cubes at all times. Additionally, many modern refrigerators are provided with anti-condensation heaters for heating selected portions of the exterior of the refrigerator cabinet, which portions might otherwise be cooled below the ambient dewpoint, resulting in unsightly condensation forming. Also, butter conditioner heaters are sometimes provided to maintain a butter compartment at a temperature slightly warmer than the remainder of the refrigerated space.
Many of the features and functions mentioned above have been provided with independent control for various reasons. For example, to minimize energy consumption, switches have been provided to turn off anti-condensation heaters during periods of low ambient humidity. For the same reason, various forms of variable defrost interval control have been developed. For example, adjustable defrost control timers have been provided which permit a user to optimize the defrosting interval for particular ambient and usage conditions. Furthermore, various so-called "demand defrost" systems have been proposed whereby the refrigerator control system itself varies the interval between successive defrosting operations depending on various sensed parameters such as door openings and ambient humidity. A simple form of demand defrost is achieved by connecting the motor in the defrost control timer such that it operates only when the refrigerator compressor is operating in response to a thermostatic temperature control. Thus, under high usage conditions when the compressor runs frequently, the defrost control timer accumulates time at a faster rate. During low usage conditions the compressor operates less frequently and the defrost control timer accumulates time at a slower rate. Automatic icemakers customarily are equipped with switches or other means to effectively turn them off when desired. Lastly, most household refrigerators include a user-adjustable thermostatic temperature control for setting a desired temperature to be maintained within at least one refrigerated compartment.
The operating conditions of the various elements of a refrigerator, being designed for normal usage conditions, are in some respects inappropriate for extended periods of non-usage of the refrigerator, such as might occur when a user is away for periods of a week or longer while on vacation ("Non-usage" and "zero-usage" are interchangeably employed herein and are intended to refer to a condition wherein the door of the refrigerator is not opened over an extended period of time, in contrast to a condition where the refrigerator is unplugged or otherwise turned off and placed into storage.)
By suitable adjustment of the refrigerator controls, an operating condition more appropriate to an extended period of zero usage might be achieved. Such an operating condition would be more appropriate both from the standpoint of avoiding unnecessary consumption of energy, and from the standpoint of decreasing the possibility of a failure which, under normal conditions of daily use would be merely an inconvenience, but which, during an extended unattended period of operation could have potentially greater consequences. While serious failures are relatively rare, on a statistical basis there is always some probability of occurrence despite good design practices.
It is therefore an object of the invention to provide a convenient means for a user to affect various operating conditions to place a refrigerator in an operating mode appropriate to a condition of zero usage.
It is a further object of the invention to provide an inexpensive means for effectively extending the interval between successive automatic defrosting operations when appropriate.